1. Field of the invention
The present invention relates to an image forming apparatus for forming an image by using a photosensitive sheet coated with microcapsules containing photohardening materials and coloring dyes and an image receiving sheet coated with developer which reacts with the coloring dyes to develop colors. More particularly, the invention relates to an image forming apparatus wherein the photosensitive sheet is wound on a roll and is accommodated in a photosensitive sheet cartridge, the photosensitive sheet cartridge being mounted in the image forming apparatus in a detachable way.
2. Description of the prior art
Japanese Laid-Open Patent Publication No. 58-88739 discloses an image forming method using a photosensitive sheet coated with microcapsules containing photohardening materials and coloring dyes and an image receiving sheet coated with developer which reacts with the coloring dyes to develop colors.
The formation of an image according to the above method is carried out as follows: when the light of an original image is projected onto the photosensitive sheet, the microcapsules harden selectively where the light strikes, forming a latent image thereon corresponding to the original image. Then, the image receiving sheet coated with developer is superimposed and pressed on the photosensitive sheet on which the latent image has been formed. This causes the unhardened microcapsules to rupture, and therefore, the coloring dyes contained therein to flow out to react with the developer on the image receiving sheet to develop colors, thus forming on the image receiving sheet an image corresponding to the original image.
In an image forming apparatus using an image forming method such as that described above, the photosensitive sheet exposed to the light from the original image is passed, with the image receiving sheet superposed thereon, between a pair of pressure rollers, thereby forming an image on the image receiving sheet. To prevent the microcapsules from rupturing by an external force or hardening by exposure to external light before exposure to the original image, the photosensitive sheet used in the image forming apparatus is accommodated in a rolled form in a photosensitive sheet cartridge which is mounted in the image forming apparatus before use. When the photosensitive sheet cartridge is mounted in the image forming apparatus, it is necessary to draw the photosensitive sheet out of the photosensitive sheet cartridge and feed it through an exposure section and then between a pair of pressure rollers while it is transported in a transport path by means of transport rollers, i.e. to load the photosensitive sheet. Therefore, if the photosensitive sheet is not aligned properly in the transport path, smooth transport of the sheet is hampered, and the photosensitive sheet may be creased or broken, or in some cases, may jam in the transport path. If the creased or broken photosensitive sheet is fed between the pressure rollers, the rollers bind because of increased loads applied thereto. As a matter of course, with the creased or broken photosensitive sheet, it is not possible to form a good image. Thus, the image forming apparatus does not function properly unless the photosensitive sheet is properly loaded.
The photosensitive sheet is made of a very thin material with low rigidity such as a polyethylene terephthalate sheet with a thickness of 25 .mu.m. Utmost care is therefore required in manual loading of the photosensitive sheet onto the transport rollers, etc., in the transport path so as not to crease or damage it. In particular, in order to pass the photosensitive sheet without creating creases between the pressure rollers to which great pressure is applied, the pressure being applied to the pressure rollers must first be released, which requires extremely troublesome work. Moreover, it is not easy work to set the pressure rollers back to the specified pressure once it is released. Passing the photosensitive sheet without creating creases between the pressure rollers to which great pressure is applied may be accomplished by passing it with reference to the contact line between the pressure rollers, but passing the photosensitive sheet with reference to the contact line between the pressure rollers requires a highly skilled technique, which is only possible with a skilled operator, and hardly possible with ordinary users of the image forming apparatus.